During the current year, this project focused on (1) the design and synthesis of peptides for immunological and structure-function relationship studies of angiotensin II type 1 (AT1) and GnRH receptor proteins; (2) design, synthesis and structure-activity relationship studies of anti-HIV peptides. AII and GnRH receptors have the seven putative domains characteristic of G protein-coupled receptors. Based on amino acid sequences deduced from cDNA encoded for AT1b, segments from both cytoplasmic and extracellular domains were selected, synthesized and conjugated to thyroglobulin or hemocyanin. In most cases, linkage of a peptide to the carrier protein was accomplished through added or existing cysteinyl residue and sulfo-SMCC cross-linker. Using six antibodies against AT1b and Western blot analysis, two species with molecular sizes Mr=66--67 kDa and 44--45 kDa were found in bovine adrenal membranes, AT1a or AT1b transfected mouse adrenal tumor cells (Y1), and rat tissue homogenates. Photoaffinity labeling of bovine adrenal membrane with 125/I--[Sar/1, (4--N/3)Phe/8]AII followed by immunoprecipitation using the same six antisera and SDS--PAGE detected a major radioactive band corresponding 66--67 kDa, indicating it as the molecular species capable of binding the AII analogue. Similarly, seven segments with length of 12- -42 residues representing various putative domains of mouse GnRH receptor cDNA deduced amino acid sequence were selected, synthesized, and conjugated to thyroglobulin for the purpose of raising antibodies against them. A peptide designated as GnRH4--42 was also synthesized for the purpose of investigating its ability to compete with the receptor for GnRH--mediated G protein coupling and PKC activation. We are synthesizing peptides covering transmembrane domains of low alpha-helical propensity sequences in AII receptors and will measure their secondary structures by circular dichroism in various conditions including aqueous buffer, helicogenic solvents and phospholipid vesicles in an attempt to understand their secondary structure. The results will indicate whether a beta-sheet structure can exist in the membrane or if a different set of rules governs the secondary structure propensities in lipid environment. A series of peptides corresponding the N--terminal portion of an anti--HIV protein, GAP 31 were synthesized and analyzed for their biological activities. A 33 amino acid segment designated as K10--K42 was found to be the shortest peptide necessary and sufficient for HIV--1 inhibition, supercoiled or viral DNA binding, viral, ribosomal or mRNA binding and ribosome inactivation. A shorter peptide (E23--K42) displayed the ribosome inactivation but not the other activities. Mapping the minimal domain of the GAP 31 offers new insights into a rational design of molecular mimetics of anti--viral drugs.